Commit 7ea7e98f authored by Matthew Wilcox's avatar Matthew Wilcox Committed by Greg Kroah-Hartman
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PCI: Block on access to temporarily unavailable pci device 



The existing implementation of pci_block_user_cfg_access() was recently
criticised for providing out of date information and for returning errors
on write, which applications won't be expecting.

This reimplementation uses a global wait queue and a bit per device.
I've open-coded prepare_to_wait() / finish_wait() as I could optimise
it significantly by knowing that the pci_lock protected us at all points.

It looked a bit funny to be doing a spin_unlock_irqsave(); schedule(),
so I used spin_lock_irq() for the _user versions of pci_read_config and
pci_write_config.  Not carrying a flags pointer around made the code
much less nasty.

Attempts to block an already blocked device hit a BUG() and attempts to
unblock an already unblocked device hit a WARN().  If we need to block
access to a device from userspace, it's because it's unsafe for even
another bit of the kernel to access the device.  An attempt to block
a device for a second time means we're about to access the device to
perform some other operation, which could provoke undefined behaviour
from the device.

Signed-off-by: default avatarMatthew Wilcox <matthew@wil.cx>
Acked-by: default avatarAdam Belay <abelay@novell.com>
Acked-by: default avatarAlan Cox <alan@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 50bf14b3

drivers/pci/access.c

+47 −28
Original line number Diff line number Diff line 
#include <linux/pci.h>

#include <linux/module.h>

#include <linux/ioport.h>

#include <linux/wait.h>



#include "pci.h"
@@ -63,30 +64,42 @@ EXPORT_SYMBOL(pci_bus_write_config_byte); 
EXPORT_SYMBOL(pci_bus_write_config_word);

EXPORT_SYMBOL(pci_bus_write_config_dword);



static u32 pci_user_cached_config(struct pci_dev *dev, int pos)

{

	u32 data;

/*

 * The following routines are to prevent the user from accessing PCI config

 * space when it's unsafe to do so.  Some devices require this during BIST and

 * we're required to prevent it during D-state transitions.

 *

 * We have a bit per device to indicate it's blocked and a global wait queue

 * for callers to sleep on until devices are unblocked.

 */

static DECLARE_WAIT_QUEUE_HEAD(pci_ucfg_wait);



	data = dev->saved_config_space[pos/sizeof(dev->saved_config_space[0])];

	data >>= (pos % sizeof(dev->saved_config_space[0])) * 8;

	return data;

static noinline void pci_wait_ucfg(struct pci_dev *dev)

{

	DECLARE_WAITQUEUE(wait, current);



	__add_wait_queue(&pci_ucfg_wait, &wait);

	do {

		set_current_state(TASK_UNINTERRUPTIBLE);

		spin_unlock_irq(&pci_lock);

		schedule();

		spin_lock_irq(&pci_lock);

	} while (dev->block_ucfg_access);

	__remove_wait_queue(&pci_ucfg_wait, &wait);

}



#define PCI_USER_READ_CONFIG(size,type)					\

int pci_user_read_config_##size						\

	(struct pci_dev *dev, int pos, type *val)			\

{									\

	unsigned long flags;						\

	int ret = 0;							\

	u32 data = -1;							\

	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\

	spin_lock_irqsave(&pci_lock, flags);				\

	if (likely(!dev->block_ucfg_access))				\

	spin_lock_irq(&pci_lock);					\

	if (unlikely(dev->block_ucfg_access)) pci_wait_ucfg(dev);	\

	ret = dev->bus->ops->read(dev->bus, dev->devfn,			\

					pos, sizeof(type), &data);	\

	else if (pos < sizeof(dev->saved_config_space))			\

		data = pci_user_cached_config(dev, pos); 		\

	spin_unlock_irqrestore(&pci_lock, flags);			\

	spin_unlock_irq(&pci_lock);					\

	*val = (type)data;						\

	return ret;							\

}
@@ -95,14 +108,13 @@ int pci_user_read_config_##size \ 
int pci_user_write_config_##size					\

	(struct pci_dev *dev, int pos, type val)			\

{									\

	unsigned long flags;						\

	int ret = -EIO;							\

	if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;	\

	spin_lock_irqsave(&pci_lock, flags);				\

	if (likely(!dev->block_ucfg_access))				\

	spin_lock_irq(&pci_lock);					\

	if (unlikely(dev->block_ucfg_access)) pci_wait_ucfg(dev);	\

	ret = dev->bus->ops->write(dev->bus, dev->devfn,		\

					pos, sizeof(type), val);	\

	spin_unlock_irqrestore(&pci_lock, flags);			\

	spin_unlock_irq(&pci_lock);					\

	return ret;							\

}
@@ -117,21 +129,23 @@ PCI_USER_WRITE_CONFIG(dword, u32) 
 * pci_block_user_cfg_access - Block userspace PCI config reads/writes

 * @dev:	pci device struct

 *

 * This function blocks any userspace PCI config accesses from occurring.

 * When blocked, any writes will be bit bucketed and reads will return the

 * data saved using pci_save_state for the first 64 bytes of config

 * space and return 0xff for all other config reads.

 **/

 * When user access is blocked, any reads or writes to config space will

 * sleep until access is unblocked again.  We don't allow nesting of

 * block/unblock calls.

 */

void pci_block_user_cfg_access(struct pci_dev *dev)

{

	unsigned long flags;

	int was_blocked;



	pci_save_state(dev);



	/* spinlock to synchronize with anyone reading config space now */

	spin_lock_irqsave(&pci_lock, flags);

	was_blocked = dev->block_ucfg_access;

	dev->block_ucfg_access = 1;

	spin_unlock_irqrestore(&pci_lock, flags);



	/* If we BUG() inside the pci_lock, we're guaranteed to hose

	 * the machine */

	BUG_ON(was_blocked);

}

EXPORT_SYMBOL_GPL(pci_block_user_cfg_access);
@@ -140,14 +154,19 @@ EXPORT_SYMBOL_GPL(pci_block_user_cfg_access); 
 * @dev:	pci device struct

 *

 * This function allows userspace PCI config accesses to resume.

 **/

 */

void pci_unblock_user_cfg_access(struct pci_dev *dev)

{

	unsigned long flags;



	/* spinlock to synchronize with anyone reading saved config space */

	spin_lock_irqsave(&pci_lock, flags);



	/* This indicates a problem in the caller, but we don't need

	 * to kill them, unlike a double-block above. */

	WARN_ON(!dev->block_ucfg_access);



	dev->block_ucfg_access = 0;

	wake_up_all(&pci_ucfg_wait);

	spin_unlock_irqrestore(&pci_lock, flags);

}

EXPORT_SYMBOL_GPL(pci_unblock_user_cfg_access);

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